How hard is the water in South San Francisco, CA?

Tap water hardness
64mg/L
3.8gpg
Moderately hard

Reported by California Water Service-S San Francisco · June 2025

CA typical
121 mg/L
EPA health violations since 2016
0
Softener for 3 people
24k grain
Data
Utility report

Tap water in South San Francisco has about 64 mg/L of hardness, which is 3.8 grains per gallon. On the USGS scale that counts as moderately hard. The number comes from California Water Service-S San Francisco, dated June 2025.

South San Francisco on the hardness scale, with nearby cities
060120180240300360+CA typical 121Burlingame: 31 mg/LBurlingame 31Foster City: 33 mg/LFoster City 33Alameda: 34 mg/LAlameda 34San Mateo: 35 mg/LSan Mateo 35Hillsborough: 36 mg/LHillsborough 36Belmont: 37 mg/LBelmont 37San Bruno: 44 mg/LSan Bruno 44Millbrae: 44 mg/LMillbrae 44Pacifica: 70 mg/LPacifica 70Daly City: 73 mg/LDaly City 73South San Francisco 64mg/L as calcium carbonate060120180240300360+CA 121Burlingame: 31 mg/LBurlingame 31Hillsborough: 36 mg/LHillsborou. 36San Bruno: 44 mg/LSan Bruno 44Millbrae: 44 mg/LMillbrae 44Pacifica: 70 mg/LPacifica 70Daly City: 73 mg/LDaly City 7364 mg/Lmg/L as calcium carbonate
Soft 0–60 mg/LModerately hard 61–120 mg/LHard 121–180 mg/LVery hard 181+ mg/L

South San Francisco sits 57 mg/L below the typical California figure of 121. Of the 10 nearest cities we track, 8 have softer water and 2 have harder. The range nearby runs from 31 mg/L in Burlingame to 73 in Daly City.

What 64 mg/L means at home

You may see faint white spots on glasses and shower doors after the water dries.

Scale builds up slowly. A kettle or coffee maker needs descaling now and then, maybe every few months.

Hardness is not a health problem, and EPA sets no limit for it. It is a matter of scale and soap.

What to do about it

Optional. Plenty of households at this level live with it and descale the kettle now and then.

Water softener

Worth a look if spots on glass bother you, or if your tankless water heater manual asks for softer water.

Carbon filter

Improves taste and removes chlorine. It leaves calcium and magnesium in place.

Softener size for South San Francisco

3 people × 75 gallons a day × 3.8 gpg = 848 grains a day. A 24,000-grain unit regenerates about every 28 days.

Size it for your household

EPA record for South San Francisco's water system

California Water Service-S San Francisco · PWSID CA4110009

No health-based violations since 2016

Serves about 62,609 people from surface water.

Health-based
0
Monitoring or reporting
0
Open now
0

TapWaterData ties South San Francisco to this system. EPA's service-area records do not name South San Francisco, so check the utility printed on your water bill.

Health-based means a contaminant above its legal limit or a missed treatment step. Monitoring and reporting violations are late or missing tests and notices. Source: EPA ECHO, 2026Q3 export, violations with periods starting 2016 or later. Full EPA record.

Questions

Is South San Francisco water hard?

Somewhat. It measures about 64 mg/L (3.8 grains per gallon), which the USGS classes as moderately hard.

What is the water hardness in South San Francisco in grains per gallon?

About 3.8 gpg. One grain per gallon equals 17.1 mg/L, so 64 mg/L divided by 17.1 gives 3.8.

What size water softener do I need in South San Francisco?

For 3 people using 75 gallons each per day, 3.8 gpg works out to about 848 grains a day. A 24,000-grain softener covers that with a regeneration about every 28 days.

Has the South San Francisco water system had EPA violations?

EPA records show no health-based violations for California Water Service-S San Francisco since 2016.

Nearby cities

All 515 cities in California

Hardness data: TapWaterData US Water Hardness (utility report, June 30, 2025), CC BY 4.0. Population: US Census Bureau. Violations: EPA ECHO. How we use them.